The present invention relates to systems for controlling venting of fuel vapors from a vehicle fuel tank, and particularly to venting apparatus which operates to seal the vapor space in the interior of a fuel tank during refueling and reopens at some point after refueling has been completed to vent the vapor space. More particularly, the present invention relates to a refueling ventilation and fill-limit system for controlling tank ventilation and for preventing overfilling of a fuel tank.
Management of fuel vapor on-board a vehicle is an important part of modern vehicle fuel system design. A tank venting control assembly for selectively discharging fuel vapor pressure in response to the development of high tank pressure conditions and for introducing air into the fuel tank in response to the development of vacuum conditions therein is disclosed, for example, in U.S. Pat. No. 5,234,013 to Roetker et al.
Fuel vapor can be created in the fuel tank by temperature differences between the fuel tank and liquid fuel from a fuel pump, as well as by sloshing and agitation of the fuel tank during normal vehicle operation. The pressure buildup resulting from the creation of new fuel vapors must be relieved properly. For this reason, many vehicle fuel systems are equipped with tank venting control assemblies capable of discharging a relatively large amount of fuel vapor in response to the development of high pressure conditions in the fuel tank.
In addition to providing for adequate fuel vapor discharge from the fuel tank during high tank pressure conditions, well-designed tank pressure control assemblies must be capable of responding to a reduction of pressure in the fuel tank to below a predetermined level. These tank vacuum conditions are usually relieved by introducing ambient air into the fuel tank to bring the fuel vapor pressure in the fuel tank back to approximately atmospheric pressure. However, it has long been problematic to provide adequate tank vacuum relief functions without complicating a tank venting control assembly unnecessarily.
It is well understood that significant quantities of fuel vapor can escape from a fuel tank through the filler neck to the atmosphere during the refueling of motor vehicles. Early attempts to control the vapor escape focused upon control devices fitted to a fuel-dispensing pump nozzle connected to a service station fuel pump. Later, control devices mounted directly on-board the vehicle (and thus referred to as "On-Board Refueling Vapor Recovery" systems or "ORVR" systems) were developed. See, for example, U.S. Pat. No. 4,816,045 to Szlaga et al., relating to a vapor-recovery system mounted on the fuel tank filler neck. ORVR systems which mount to a fuel tank have also been developed as shown, for example, in U.S. Pat. No. 5,156,178 to Harris.
In addition to controlling vapor escape, well-designed ORVR systems also assist in controlling the amount of liquid fuel which can be pumped into the fuel tank during refueling. For safety reasons, fuel systems are designed so that the fuel tank is never completely filled with liquid fuel. Rather, at least a predetermined portion of the space inside the fuel tank is left for liquid fuel and fuel vapor expansion. Although fuel pump nozzles typically include sensors for shutting off the flow of liquid fuel into the fuel tank when the fuel tank is nearly filled, fuel pump users may manually override the sensors by continuing to pump fuel after the sensors have automatically and temporarily shut the pump nozzle off. To assist in preventing tank overfill under such conditions, an ORVR system is usually provided with a "fill-limit" control system which assists in triggering the nozzle shut-off mechanism when the level of liquid fuel in the fuel tank has risen to a predetermined level. See, for example, the fill-limit control systems disclosed in U.S. Pat. No. 4,816,045 to Szlaga et al and U.S. application Ser. No. 08/241,186, filed May 11, 1994 to Harris.
It has also long been recognized that fuel vapor is generated in the fuel tank during operation of the vehicle, for example, by evaporation or by sloshing of the liquid fuel against the walls of the tank. Excessive pressure can build up in the fuel tank as a result of the newly formed fuel vapor unless control devices are provided to vent the fuel vapor from the fuel tank during vehicle operation. Such valves have been referred to as "run-loss" valves or tank-venting rollover valves because they handle fuel vapor loss during vehicle run and are capable of preventing liquid fuel carryover during vehicle rollover.
Fuel pump nozzles are known to include a fill-limiting sensor for shutting of the flow of fuel from the nozzle when the fuel tank is nearly filled. Typically, this fill-limiting sensor is triggered whenever the fuel tank is full and fuel "backs up" the filler neck to splash onto or reach the fill-limiting sensor located on the nozzle. Sometimes fuel pump operators overfill a fuel tank inadvertently in a good-faith effort to fill the tank "completely" or to purchase a quantity of fuel that can be paid for in cash without causing the operator to receive unwanted coinage in change.
It has been observed that fuel pump operators are able to manually override or bypass some fill-limiting sensors on nozzles by continuing to pump fuel after the pump nozzle has automatically shut off several times. This practice has come to be called the "trickle-fill" method of introducing liquid fuel into a fuel tank. Using this well-known trickle-fill method, the fuel pump operator "clicks" or squeezes the lever handle on the pump nozzle slowly two or three times in succession after automatic nozzle shut-off has occurred in order to introduce more fuel into the fuel tank without actuating the fill-limiting sensor right away. It will be appreciated that such trickle-fill practices can result in overfilling the fuel tank which can effectively reduce the fuel vapor expansion capacity in the vapor space available within the filled fuel tank.
Vehicle fuel systems are known to include valves for venting the vapor space in a fuel tank. See, for example, U.S. Pat. Nos. 4,760,858; 4,991,615; and 5,028,255.
What is needed is a fill-limit and tank ventilation control system that is able to vent fuel vapor from the vapor space in a fuel tank during early stages of refueling but block introduction of any and all liquid fuel in excess of a maximum volume so as to preserve a minimum volume of the vapor space in the fuel tank once the fuel tank is filled to its maximum capacity with fuel. Ideally, this fill-limit and tank ventilation control system could be included as one component in a comprehensive On-Board Refueling Vapor Recovery (ORVR) vehicle fuel system. An ORVR system is used to manage fuel vapor recovery during all phases of vehicle use. In addition, a fill-limit control system that is adaptable to permit customers some latitude to trickle-fill their fuel tanks without overfilling the fuel tanks would be welcomed by fuel customers and vehicle makers.
It will be understood that each vehicle has a custom-designed fuel tank sized and shaped to mount onto a particular vehicle underbody. That being the case, one can begin to understand why a single fill-limit and tank ventilation valve assembly might not be of the proper size to fit into every custom-designed vehicle fuel tank. It will be understood that certain "tall" (i.e., vertical height) valves do not fit well in small-capacity, compact vehicle fuel tanks characterized by short vertical height. Few vehicle manufacturers wish to carry in inventory a separate valve assembly for each manufactured vehicle. What is needed is a modular fill-limit and tank ventilation valve assembly that can be adapted easily to fit into a wide variety of vehicle fuel tanks.
Vehicle manufacturers would welcome a modular fill-limit and tank ventilation valve assembly that could be assembled using a series of standardized parts to produce tall, short, or medium height valve assemblies to produce a "customized" valve assembly that is sized to fit properly in a vehicle fuel tank of a particular size and shape. In such a system, all components including valves would be standardized and modularized and other modular components would be used to connect the standardized valve components together so as to establish a customized vertical height for each modular fill-limit and tank ventilation valve assembly. System costs could be minimized and manufacturing schedules could be improved if such a modular valve assembly could be configured.
According to the present invention, a venting control system is provided for controlling discharge of fuel vapors from a vehicle fuel tank. The venting control system includes a vent apparatus mountable in an aperture formed in a top wall of the fuel tank. The vent apparatus is formed to include a vapor inlet opening communicating with an interior region of the fuel tank, a vapor outlet opening, and a passageway interconnecting the vapor inlet opening and the vapor outlet opening. The system further includes a tubular skirt having an uppermost end coupled to the vent apparatus and a lowermost end arranged to extend downwardly away from the vent apparatus and a fill-limit valve assembly coupled to the lowermost end of the tubular skirt. The tubular skirt and the fill-limit valve assembly are positioned to lie in the interior region of the fuel tank when the vent apparatus is mounted in the top wall aperture of the fuel tank.
Pressurized fuel vapor in a fuel tank carrying a venting control system in accordance with the present invention is vented from the fuel tank to a vapor-recovery canister or other destination through channels and passageways formed in the tubular skirt and the vent apparatus. In preferred embodiments, the vent apparatus includes a pressure-relief and vacuum-relief valve assembly and a rollover valve assembly for regulating flow of fuel vapor, air, and liquid fuel into and out of the fuel tank through the venting control system.
Also in preferred embodiments, the lowermost end of the tubular skirt is formed to include a skirt inlet for admitting pressurized fuel vapor and liquid fuel from the fuel tank into a channel formed in the tubular skirt and coupled to the vapor inlet opening formed in the overlying vent apparatus. The fill-limit valve assembly is coupled to the lowermost end of the tubular skirt and configured to control flow of pressurized fuel vapor and liquid fuel from the fuel tank into the tubular skirt channel.
The fill-limit valve assembly illustratively includes a fill-limit valve housing having an interior region and a float valve contained therein. The float valve is movable in the interior region of the fill-limit valve housing between an opened position allowing flow of fuel vapor and liquid fuel from the fuel tank into the channel in the tubular skirt through the skirt inlet and a closed position preventing flow of fuel vapor and liquid fuel from the fuel tank into the channel in the tubular skirt through the skirt inlet. The buoyant float valve is moved by rising liquid fuel in the fuel tank to its closed position at a late stage during tank refueling to block gross passage of liquid fuel into the channel formed in the tubular skirt through the skirt inlet. Thus, the float valve functions to prevent liquid fuel from exiting the fuel tank through the tubular skirt and the vent apparatus in the venting control system in accordance with the present invention during refueling.
Another aspect of the present invention is that the venting control system illustratively includes snap-connected modular components. This modular venting control system comprises a standardized vent apparatus, a standardized fill-limit valve assembly, and tubular skirts of many different lengths. In use, a venting control system sized to fit in a particular custom-designed fuel tank can be made by interconnecting the standardized vent apparatus and fill-limit valve assembly using a tubular skirt having an appropriate length. Assembly of these modular parts is made easy by using a first snap-connector to couple the uppermost end of the tubular skirt to the overlying vent apparatus and a second snap-connector to couple the lowermost end of the tubular skirt to the underlying fill-limit valve assembly.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.